In September three jetliners-- one American, one British and one Swiss-- were hijacked by Palestinian Arabs to Jordan. The passengers were held hostage. This action further undermined the sovereignty of King Hussein's government. The King decided to take action and fighting broke out between the Jordanian Army and the Palestine Liberation Organization. The Syrians attempted to intervene on the side of the P.L.O. but Israel warned that they, too, would then intervene. The Jordanian army defeated the P.L.O. whose forces fled to Lebanon.